Pavement of roads is largely divided into impermeable pavement and permeable pavement. Asphalt pavement and ready-mixed concrete pavement are examples of the impermeable pavement, through which rain or water does not sink into the ground, thus reducing the time for the rain to flow into the river or stream and increasing the likelihood of flooding. Also, such impermeable pavement causes draining of underground water, and causes environmental issues such as so-called heat island effect due to the increase of surface area.
Therefore, the permeable pavement has come into use more widely, especially on sidewalks, bicycle paths, squares, etc.
In general, a permeable concrete pavement comprises aggregates of the size generally less than 13 mm to maintain suitable porosity and strength, allowing water or rain to seep into the ground through pores among the aggregates and fostering the growth of trees and plants around the pavement. It also prevents flooding of the river by allowing heavy or torrential rain to flow under the earth. Further, as the rain or water does not stay on the permeable concrete pavement, it provides less slippery and much safer walking, jogging or driving conditions.
Such conventional permeable pavement is divided into a permeable asphalt concrete and a permeable cement concrete. However, the asphalt concrete has disadvantages in that the surface deforms considerably due to high temperatures during the summer season and the pores get clogged up due to the viscosity of the asphalt. Also, the cement concrete is so rigid that people get hurt when they fall upon it.
In addition, the conventional permeable-concrete pavement is covered with epoxy pigments for cosmetic view of the surface, but a ramp covered with such epoxy pigments is more slippery than a normal concrete pavement, causing problems in safety. Further, when the pores are covered with dust, permeability deteriorates, thus increasing maintenance costs for declogging the pores, i.e. removal of the dust.
As for the permeable cement concrete, there have been disadvantages of efflorescence, i.e. whitening effect, by which soluble cement components move to the surface of the concrete together with moisture and turn out to be white educt; cracking caused by its coefficient of contraction and expansion larger than normal concrete (if line cutting is not done before curing, for example, within 24 hours after pouring the concrete); swelling (rising) which occurs in winter by the frozen water's increase in volume and its rising or extending above the surface of the earth; and segregating or breaking of the aggregates of the pavement caused by calcium chloride scattered on roads in winter.
Therefore, various attempts to improve the disadvantages of the conventional permeable concrete have been suggested.
For example, in order to prevent the whitening effect, the permeable cement was hardened closely by lowering the ratio of water, or waterproof agents such as stearic acid and paraffin emulsion were added to suppress the movement of moisture.
In order to prevent the cracks, interval of the line cutting was shortened and fiber was reinforced. Also, for the prevention of swelling, a drainage way was made to lower the level of underground water, or a granular layer was provided above the level of underground water to block the capillary rise.
However, decisive and clear solutions to these disadvantages have not yet been suggested.
The inventor of the present invention studied and researched into materials for permeable concrete pavements, and as a result, the inventor completed the present invention by using charcoal dust and particulates of blast furnace slag obtainable as a by-product in an iron and steel mill, to overcome disadvantages of the conventional permeable concrete, thus resulting in production of a permeable concrete having excellent strength and permeability.
In general, charcoal is a black, porous, carbonaceous material comprising 85% of carbon, 10% of moisture and 3% of mineral such as calcium, potassium, magnesium and iron, etc. and is produced by the destructive distillation of wood (carbonation) at the temperatures of 600-900° C. It is odorless and tasteless. If the charcoal is looked into through an electron microscope, it has numerous micropores in a micron unit, which influence the sectional area of the charcoal in contact with the air. Surprisingly, 1 g of the charcoal has about 297 m2 sectional area, which means that charcoal has excellent permeability and water retention ability. The charcoal having such a large surface area can be used to adsorb gases as a deodorizing agent or to absorb impurities, and also can be used as an antiseptic by preventing against putrefaction.
Meanwhile, the blast furnace slag is obtained in producing pig iron from iron ore in a blast furnace, and the slag's fineness significantly improves viscosity and fluidity of concrete and reduces bleeding. If particulates of the blast furnace slag having high fineness are substituted for about 30-50% of normal concrete, the strength of the cement can be greatly increased. Therefore, the blast furnace slag can be useful in high-rise reinforced concrete buildings or in concrete construction for lower stories of reinforced-concrete towers or basement construction.